My personal trainer told me that i should get an iron supplement since i am on a vegan diet, and a female.

Unless your personal trainer is also your physician, don't take this advice. Iron is a dangerous supplement, you can die from taking too much iron, which is very easy to do. One pill could be an overdose. No one should supplement with iron unless specified by a doctor after blood work. A vegan diet is not deficient in iron. Most people eating a vegan diet get more iron than meat eaters. Talk to your doctor and get blood work done. I say this as a personal trainer myself.